1. Field of the Invention
The present invention relates to an electrophotographic printer.
2. Related Art
There has been proposed an electrophotographic printer that forms images on a recording sheet. FIG. 1 shows main components of such an electrophotographic printer 1. When a printing process starts, first, an external controller (not shown) outputs a print start command to the electrophotographic printer 1. In response to the print start command, a photosensitive-drum driving motor 131 starts rotating a photosensitive drum 101. When the rotation speed (peripheral velocity) of the photosensitive drum 101 reaches a predetermined process speed, the controller outputs a synchronization-sheet-feed signal (hereinafter referred to as “CPF-N signal”).
In response to the CPF-N signal, an irradiation process starts for irradiating a light beam onto the photosensitive drum 101 at an irradiation point EP for forming an electrostatic latent image thereon. A visible toner image corresponding to the electrostatic latent image is developed on the photosensitive drum 101, and then transferred at a transfer point TP onto a web W.
In response to the CPF-N signal, a preparation process is started also. That is, a switching motor 109 brings a pressure roller 13c into contact with a heat roller 13b, and then the rotation speed of the heat roller 13b is accelerated to the process speed. Also, a belt driving motor 107 rotates a web transport belt 8 so as to accelerate a web transfer speed of the web W to the process speed.
FIG. 2 shows a timing chart of the above-described preparation process. Here, a distance L is a moving distance of the photosensitive drum 101 from the irradiation point EP to the transfer point TP with respect to a rotation direction B of the photosensitive drum 101. A time T1 indicates a time duration that the photosensitive drum 101 takes to move by the distance L. The time T1 is expressed in a following equation:T1=L/S
wherein L is the moving distance of the photosensitive drum 101 from the irradiation point EP to the transfer point TP; and
S is the process speed.
As shown in FIG. 2, when a CPF-N signal is received, a control unit 120 (FIG. 5) of the electrophotographic printer 1 generates a pressure-roller driving signal (hereinafter referred to as “BR DRV-P signal”) so as to bring the pressure roller 13c into contact with the heat roller 13b. Subsequently, the control unit 120 generates a sheet-feed signal (hereinafter referred to as “PAPER FEED-P signal”) so as to accelerate the web transport belt 8 to the process speed. When the pressure roller 13c is brought into contact with the heat roller 13b, the control unit 120 generates a heat-roller-driving signal (hereinafter referred to as “HR ROT-P signal”) so as to accelerate the rotation speed of the heat roller 13b to the process speed.
This preparation process in the electrophotographic printer 1 takes a time T2 and completes before the time T1 elapses after the CPF N signal was generated, that is, before the toner image developed on the photosensitive drum 101 reaches the transfer point TP.